Multi-turn optical encoders are employed in many different applications. The mechanical construction of multi-turn optical encoders is usually based on gear train design, where gears with openings or holes must be provided for light to pass through the gears for subsequent collimation, reflection or detection. The openings or holes often prevent the gears in optical encoders from being packed very close to one another, and also limit the precision that may be obtained for injection-molded gears. In addition, substrates such as printed circuit boards, flexible cables and the like are typically required on both sides of the gear train to impart the required mechanical integrity to such optical encoders. Finally, multi-turn optical encoders are typically incapable of sensing partial revolutions of the constituent disks or gears disposed therein.
Magnetic multi-turn encoders are also known in the art, but are easily affected by external magnetic fields and cannot operate at very high temperatures without being demagnetized. Such characteristics obviously limit the type and number of applications in which magnetic multi-turn encoders may be used.
What is needed is a multi-turn encoder that may be made more compact, manufactured at lower cost and with higher precision, and permit partial revolutions of constituent disks to be sensed and measured.